This invention relates to a web-marking apparatus for marking (e.g. notching) an edge of an elongated web, particularly (but not exclusively) for marking a longitudinal edge of a strip of photographic film.
Equipment of the general type here under discussion is used in the photographic field for various purposes. For example, in modern film-processing laboratories it is customary to develop a whole series of films (each film may come from a different customer) and thereafter to connect the individual films endwise so as to form a long (composite) strip of film which is then passed through automated copying machinery (a printer). In preparation for this printing operation the equipment here under discussion may be used to form in a longitudinal edge of the long film strip a notch opposite each film frame to be copied; these notches are then sensed and thus serve to control the operation of the printer and/or associated devices, e.g. to determine where the respective film frame must be located before printing begins. Another use of such equipment is to form film strip edges with notches which then serve (e.g. in a press-splicer) for splicing-together undeveloped films to identify where film strips (or sections thereof) are to be spliced together.
According to a prior-art proposal the film strip(s) is (are) photoelectrically scanned to determine where the blank (transverse) film portions are located which separate successive film frames from one another. Whenever one of these portions is sensed, a signal is generated which triggers operation of the notching equipment. The notching itself is usually performed by a reciprocating die or punch.
To be notched properly the web must be guided at least at one edge. The prior art proposes to pass the web or film through a flat (i.e. relatively wide but low) channel the width of which corresponds about to the web width. Some webs and most films tend to bow in transverse direction, i.e., intermediate their longitudinal edges. The channel eliminates the bowing and flattens the web so that the web enters the notching station in more or less proper position. However, unless at least one side edge is always in a predetermined position when the web is in the notching station, it is impossible to assure that all successive notches are of the same size and depth. The channel can be made flat enough to meet this requirement, but this brings with it the danger that dust particles and other contaminants in the channel damage the web, i.e. scratch the surface of the web in a photographic film. Such scratches can, incidentally, also develop as the edges of the film scrape along the lateral walls of a (film-guide) channel.
Another proposal of the prior art engages that longitudinal edge of a film which is not being notched, i.e. the one opposite the edge which is being notched, under spring pressure in order to urge the film transversely of the path of movement and to bias the edge-being-notched against a locating abutment of the notching station. This improves the edge-positioning of the film in the notching station but drastically increases the danger of film scratching because it bows the film transversely under the spring pressure so that the longitudinal center part of the film (due to the bowing at the highest point) engages the wall bounding the film channel and can become scratched.